
public class creatTreeByPreAndIn {

    public static class TreeNode {
        int val;
        TreeNode right;
        TreeNode left;

        TreeNode(int val) {
            this.val = val;
        }
    }
        int preIndex = 0;
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        return buildTreeChild(preorder,inorder,0,inorder.length - 1);
    }

    public TreeNode buildTreeChild(int[] preorder,int[] inorder,int inbegin,int inend){

        if(inbegin > inend) return null;

        TreeNode root = new TreeNode(preorder[preIndex]);

        int findIndex = findIndex(inorder,inbegin,inend,preorder[preIndex]);

        preIndex++;

        root.left = buildTreeChild(preorder,inorder,inbegin, findIndex - 1);

        root.right = buildTreeChild(preorder,inorder,findIndex + 1,inend);

        return root;

    }

    public int findIndex(int[] inorder,int inbegin,int inend,int key){

        for(int i = inbegin;i <= inend;i++){
            if(inorder[i] == key){
                return i;
            }
        }
        return -1;
    }
}
